Digital synthesizers or other electronic systems that create music or other sound can often be utilized as an electronic musical instrument or electronic sound machine. A digital synthesizer is often arranged to accept signals from a musician or operator interface and to produce digital output signals that represent analog signals in the audio frequency range. A digital synthesizer is also frequently arranged to accept pre-recorded sequences of music events in a Musical Instrument Digital Interface (MIDI) format.
A digital output signal from a digital synthesizer can be converted to an analog signal and delivered to equipment, such as a loudspeaker, tape recorder, mixer or other similar device, to reproduce the signals as intelligible sound. The digital synthesizer can be arranged to provide output signals that simulate the sounds of one or more conventional musical instruments. Alternatively, the synthesizer can be arranged to simulate sounds that would be emitted by a theoretical instrument having predetermined audio characteristics that are partly or wholly different from the corresponding characteristics of any convention, known instrument.
For previous synthesizers, synthesis of music and other sounds is a formidable task. A real musical instrument produces a complex blend of many different frequencies and impart what is commonly referred to as “tone color” or “timbre” to the associated sound. For example, a percussion sound made by a drum or cymbal is an aperiodic sound that cannot be fully described by any simple mathematical function. Accordingly, the reproduction or synthesis of digital signals representing sounds as rich and complex as a real musical instrument is a formidable task for digital signal sampling and processing. Ideally, the synthesizer should respond to the nuances of a musician's manipulation of the interface (e.g., a particular musical instrument). For example, a snare drum has many different audio characteristics when played in different locations, such as adjacent to the center of the drum membrane, adjacent to the rim, or on the rim of the drum. Additionally, the audio characteristics of a percussion instrument will vary with the striking force and stylistic inflection of the musician.
By providing a large enough waveform database, more realistic and expressive synthesis of a given group of sounds can be achieved. Many synthesizers relying on waveform sampling technology are used extensively in the music and multimedia fields for their ability to create musical sounds that closely emulate the sound of a musical instrument.
At present, a digital synthesizer system often utilizes a MIDI to control the synthesizer. The MIDI interface creates control signals or other MIDI control data. The MIDI control data may represent a music event, such as occurrence of specific musical notes from a particular musical instrument, such as a piano, drum or horn. However, MDI has some fundamental limitations. For example, a synthesizer that uses a MDI notation has trouble recreating a human voice.
A conventional synthesizer system utilizes a large solid state memory that stores the digital waveform signals representing each note played on a particular instrument. The memory can be a static random access memory (SRAM), a dynamic random access memory (DRAM), a read only memory (ROM) or some other similar memory with sufficiently rapid response. When a musician actuates a key or other interface device, the appropriate waveform is selected, depending upon the key actuated and upon the intensity and velocity of the key strike. The waveform is then converted into an analog output signal for sound reproduction. A digital waveform signal can be combined with other waveform signals that represent other musical notes being displayed, before the conversion to an analog output signal.
In this arrangement, the synthesizer, in effect, merely plays back digital recordings of individual musical notes or other sounds. Each waveform signal is stored as a collection of individual data words, each representing a single sample of the waveform at a particular time.
A sequencer is a device for editing musical data, such as MIDI events, and converting the musical data into a musical signal in real time. Synthesizers are frequently used together with a computer to play a musical score. In this arrangement, a sequencer reads a MIDI file as an ordered sequence. However, it is generally recognized that MDI files and synthesizers are unable to recreate the nuances in a recording or to capture the background noises of a live audience.
Other prior art systems store only one or a relatively few waveform signals representing each musical instrument. These stored waveforms are then adjusted by digital signal processing or other electronic techniques, such as nonlinear distortion, to reflect the frequency and amplitude changes associated with particular musical characteristics, as indicated by the MIDI control data. For example, the frequency and amplitude of a sample waveform representing middle C on a piano can be adjusted to synthesize a different piano note and volume. However, these synthesizers are unable to (re)produce the complex blends or tone color with high enough fidelity for the musically trained ear.
In another approach, some systems use digital filtering to adjust the harmonic content of a particular note. However, these systems require a large amount of computer power and can be affected by audio quality degradation.
What is needed is an audio synthesizer system that can reliably reproduce all types of sounds, including music and the human voice. Preferably, the system should allow a separation of music or other information-bearing sound into two or more selected components, where no single component allows reproduction of sounds resembling the original sounds. Preferably, the system should allow encryption or other encoding of one or more of the selected components and should allow change of parameters affecting the format of one or more of the components.